On December 10, 2022 Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), reported that its research collaborators at Fred Hutchinson Cancer Research Center presented data from the Compassionate Use Program on anti-leukemic activity of STRO-002, a novel folate receptor-α (FR-α) targeting ADC, in pediatric patients with relapsed/refractory CBFA2T3-GLIS2 (CBF/GLIS) acute myeloid leukemia (AML), commonly known as RAM phenotype AML, in an oral presentation at the 64th American Society of Hematology (ASH) (Free ASH Whitepaper) Annual Meeting and Exposition (ASH 2022) in New Orleans, LA (Press release, Sutro Biopharma, DEC 10, 2022, View Source [SID1234625064]).

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STRO-002 was provided to 17 pediatric patients with CBF/GLIS subtype AML on a compassionate use basis. Clinical results from these patients were compiled by Sutro and presented as an oral presentation by Soheil Meshinchi, M.D., Ph.D., Professor, Clinical Research Division, at Fred Hutchinson Cancer Research Center; Professor, Division of Pediatric Hematology-Oncology, at the University of Washington School of Medicine; and Principal Investigator for the program, titled, "Anti-Leukemic Activity of STRO-002 a Novel Folate Receptor-α (FR-α)-Targeting ADC in Relapsed/Refractory CBFA2T3-GLIS2 AML."

"I am heartened to observe such encouraging results in children with this rare disease who have a dismal prognosis with conventional therapies and no treatment options," commented Dr. Meshinchi. "The clinical responses to STRO-002 in this group of patients who have relapsed or are refractory to standard of care treatments, suggest that this drug is particularly promising and provides hope for patients and families impacted by this devastating disease."

CBF/GLIS subtype AML is a rare, serious and life-threatening disease affecting pediatric patients with a median age of 1.5 years1 and the prevalence of CBF/GLIS in childhood is approximately 1 to 3% of pediatric AML cases1. These high-risk children with AML have an extremely poor prognosis with a 5-year overall survival of approximately 20%2. Patients are highly refractory to standard of care therapies and there are currently no approved therapies specifically targeting CBF/GLIS subtype AML.

Recent studies have shown that FOLR1, which encodes for FolRα, is silent in normal hematopoiesis, but is uniquely induced by the CBF/GLIS fusion3. Preclinical data presented last year at ASH (Free ASH Whitepaper) 2021 demonstrated that patients with CBF/GLIS AML may benefit from STRO-002.

"We are encouraged by the positive results of our compassionate use program in children with a rare form of AML with STRO-002, which was recently granted Orphan Drug Designation by FDA in this patient population," said Bill Newell, Sutro’s Chief Executive Officer. "These results underscore our confidence in the efficacy and tolerability for STRO-002, in addition to the development path forward for patients with ovarian and endometrial cancers."

ASH 2022 Data Highlights:

17 pediatric patients were treated with STRO-002 on a compassionate use basis.
All 17 patients were relapsed/refractory to standard of care AML treatments. The median age of the patients is two years old and the median number of prior therapies is two. Eight of the patients had previously undergone a stem cell transplant (SCT).
STRO-002 was well-tolerated as a monotherapy agent and in combination with standard of care therapies.
In the 17 patients treated, Best Overall Response (BOR) includes eight patients with complete remission (CR), of which seven patients were minimal residual disease (MRD) negative.
47% of the patients achieved complete remission and 53% of the patients achieved partial response or stable disease.
Responders were seen in various settings including in patients with or without prior stem cell transplant and in monotherapy or in combination with cytotoxic therapy.
The presentation will be made available today in the "Clinical/Scientific Presentation and Publication Highlights" section of Sutro Biopharma’s website at www.sutrobio.com and a whitepaper with details about this rare indication and Sutro’s compassionate use program is available on the Company’s website here.

*1: National Institutes of Health [NIH], 2022; Quessada et al 2021; Masseti et al 2019
*2: Smith JL, et al. Comprehensive Transcriptome Profiling of Cryptic CBFA2T3-GLIS2 Fusion-Positive AML Defines Novel Therapeutic Options: A COG and TARGET Pediatric AML Study. Clin Cancer Res. 2020 Feb 1;26(3):726-737. doi: 10.1158/1078-0432.CCR-19-1800. Epub 2019 Nov 12. PMID: 31719049; PMCID: PMC7002196.
*3: Le Q, et al. Targeting FOLR1 in High-Risk CBFA2T3-GLIS2 AML with Stro-002 FOLR1-Directed Antibody-Drug Conjugate, Blood, Volume 138, Supplement 1, 2021, Page 209, ISSN 0006-4971, View Source

About STRO-002

STRO-002 is an optimized FolRα-targeting antibody-drug conjugate (ADC) with a drug-antibody ratio (DAR) of 4, which is precisely conjugated using non-natural amino acids attached to stable protease-cleavable linkers and hemiasterlin-derivative warheads. STRO-002 potentially has a dual mechanism of action against the tumor through cytotoxic killing and through inducing immunogenic cell death. STRO-002 was designed with Sutro’s proprietary cell-free protein synthesis and site-specific conjugation platform, which enables precise design, rapid empirical optimization, and manufacture of site-specific homogenous ADCs.